OF THE SMOKE OF A TOWN.

Smoke is seen better and more distinctly on the Eastern side than on
the Western when the sun is in the East; and this arises from two
causes; the first is that the sun, with its rays, shines through the
particles of the smoke and lights them up and makes them visible.
The second is that the roofs of the houses seen in the East at this
time are in shadow, because their obliquity does not allow of their
being illuminated by the sun. And the same thing occurs with dust;
and both one and the other look the lighter in proportion as they
are denser, and they are densest towards the middle.